Automatic volume control system



Sept. 19, 1939. R BRADEN 2,173,248

AUTOMATIC VOLUME CONTROL SYSTEM Filed March 22, 1938 2 Sheets-Sheet 1 Zimmztor Rene H. Braden Gttofney Sept. 19, 1939. R. A. BRADEN AUTOMATIC VOLUME CONTROL SYSTEM 2 Sheets-Sheet 2 Filed March 22, 1938 ZSnventor Rene H. Braden (Ittorneg Patented Sept. 19, 1939 UNITED STATES i ATENT OFFICE Rene A. Braden, Collingswood, N. .l., assignor to Radio Corporation of America, a corporation of Delaware Application March 22, 1938, Serial No. 197,369

8 Claims.

This invention relates to systems for automatically controlling the volume of vacuum tube amplifiers or the like, and has for its principal object the provision of an improved apparatus 5 and method of operation whereby the automatic volume control potential is rendered independent of signal modulation, and distortion of the signal by the automatic volume control potential is avoided.

To this end, separate detectors are provided for the signal and for automatic volume control; a control channel including an amplifier and a detector is provided; the input circuit of the control circuit amplifier is subjected to an adjustable part of the signal channel potential and to a unidirectional bias potential which is the resultant difference of an adjustable fixed potential derived from the socket power supply unit and a potential derived from a resistor connected in the output circuit of the signal channel detector; and an automatic volume control potential derived from a resistor connected in the output circuit of the control channel detector is applied to the input circuits of the signal channel amplifiers.

Under these conditions, the control channel amplifier is biased to cut-off when the signal level is low. As the signal level increases, however, both the bias potential derived from the signal channel detector output circuit and the level of the signal applied to the input circuit of the control channel increase. This increase in signal level and bias potential eventually reaches a point at which the control channel amplifier starts to operate and an automatic volume control potential ismade available at the control channel detector output resistor. As will be readily understood by those skilled in the art, adjustment of the fixed biased potential derived from the socket power supply unit and of the level of the signal applied to the input circuit of the control channel amplifier has the advantage that the automatic volume control potential is readily controlled independently of the signal modulation and without the signal distortion which results when the automatic volume control potential is derived from the signal channel detector.

The invention will be better understood from the following description considered in connection with the accompanying drawings and its scape is indicated by the appended claims.

Referring to the drawings,

Figure l is a wiring diagram of an automatic volume control system made in accordance with the invention, and

Figure 2 is a similar diagram of an automatic volume control system including a modified control channel and control channel coupling to the signal, channel amplifier output circuit.

The system of Fig. 1 includes a signal channel comprisin intermediate frequency amplifiers ill and H, a detector l2 and an audio frequency amplifier l3. The functions performed by the various tuning capacitors, by-pass capacitors and filtering resistors are well known and these various elements need not, therefore, be given detailed consideration. As will be apparent, signal impulses applied to the input circuit of the amplifier ID are amplified by the amplifiers l and H, the amplified signal is detected by the detector 12 and the detected signal is applied through a detector output resistor i l, a coupling capacitor l5 and a coupling resistor I6 to the input circuit of the audio frequency amplifier l3.

The control channel includes an amplifier l1 and a detector l8 which is coupled to the amplifier ll through a transformer l9 and is provided with an output automatic volume control resistor 20. The amplifier I1 is preferably of the remote cut-off or variable mu type such as the Radiotron 6D6,'for example. It will be noted that the input circuit of the control circuit amplifier is coupled to the output circuit of the signal channel amplifier H through capacitors 2i and" 22 and the adjustable terminal of a resistor 23 whereby the signal may be applied to this input circuit at any desired level. Automatic volume control potential developed in the resistor 20 is applied to the input circuits of the amplifiers l0 and Il through a lead 24.

Unidirectional bias potential for the input circult of the control channel amplifier Ill is derived in part from an adjustable section of the output resistor 25 of a socket power supply unit 26 and in part from the signal channel detector output resistor M. The circuit through which this unidirectional bias potential is applied is traced from the cathode of the amplifier ll through the ground connection of the resistor 25, the resistor 25, the lead 21, the resistor M, the filter resistor 28, the lead 29, the resistor 23 and the lead 30. It will be noted that the potential derived from the resistor 25 is of negative polarity while the potential derived from the resistor I4 is of positive polarity. As previously explained, these bias potentials are so related with one another and with the signal potential applied through the resistor 23 that the amplifier I1 is biased to cutoff at low signal levels and operates to automatically control the signal volume at higher signal levels.

The control channel of Fig, 2 differs from that I of Fig. 1 in that (1) the amplifier and detector are enclosed within the same receptacle 3| and (2) the capacitor 22 is connected between the resistor 23 and the grid of the control channel amplifier. This modification of the invention operates as pointed out in connection with Fig. 1. It differs from that of Fig. 1 in that the signal is applied to the amplifier input through the capacitor 22.

I claim as my invention:

1. In a sign-a1 channel including an amplifier provided with an output circuit and a detector provided with an input circuit connected to said output circuit, the combination of a control channel, means for applying to the input of said control channel an adjustable part of the potential of said output circuit, means for applying to said control channel input a unidirectional bias potential which is the resultant difference of a fixed potential and a potential dependent on the output level of said detector, and means interconnecting the output of said control channel and the input of said amplifier for regulating the level of said signal channel.

2. In a signal channel including an amplifier provided with an output circuit and a detector provided with an input circuit connected to said output circuit, the combination of a control channel, means for applying to the input of said control channel an adjustable part of the potential of said output circuit, means for applying to said control channel input a unidirectional bias potential which is the resultant difierence of a fixed potential and a potential dependent on the output level of said detector, means for adjusting the magnitude of said fixed potential, and means interconnecting the output of said control channel and the input of said amplifier for regulating the level of said signal channel.

3. In a signal channel including an amplifier provided with an output circuit and a detector provided with an input circuit connected to said output circuit, the combination of a control channel including an amplifier and a detector connected to the output of said control circuit amplifier, means for applying to the input of said control channel amplifier an adjustable part of the potential of said signal channel amplifier output circuit, means for applying to said control channel amplifier input circuit a unidirectional bias potential which is the resultant difference of a fixed potential and a potential dependent on the output level of said signal channel detector, and means interconnecting the output of said control channel detector and the input of said signal channel amplifier for regulating the level of said signal channel.

4. In a signal channel including an amplifier provided with an output circuit and a detector provided with an input circuit connected to said output circuit, the combination of a control channel including an amplifier and a detector connected to the output of said control circuit amplifier, means for applying to the input of said control circuit amplifier an adjustable part of the potential of said signal channel amplifier output circuit, means for applying to said control channel amplifier input circuit a unidirectional bias potential which is the resultant difference 'of a fixed potential and a potential dependent on the output level of saidsignal channel detector, and means including a resistor common to the control circuit detector output circuit and said signal channel amplifier input circuit for regulating the level of said signal channel.

5. The combination with a signal channel including an amplifier provided with an output circuit and a signal detector provided with an input circuit connected to said output circuit, of a control channel connected in parallel with said signal channel, and including means for applying to the input of said control channel an adjustable part of the potential of said output circuit, means for applying to said control channel input a unidirectional bias potential which is the resultant difference of a fixed potential and a potential dependent on the signal output level of said detector, and means interconnecting the output of said control channel and the input of said amplifier for regulating the level of said signal channel.

6. In a radio signal amplifying system, means providing a. signal amplifying channel, a signal detector in said channel providing means for deriving a unidirectional biasing potential from said detector, a control channel coupled to said signal amplifying channel in parallel relation thereto, and including a signal amplifier device and a rectifier coupled thereto, means for applying the unidirectional output voltage from said rectifier to said signal amplifying channel to control the gain therein, means for applying said first-named unidirectional biasing potential to said signal amplifying device in the control channel in opposition to a fixed potential, and means in circuit with said amplifier device providing said fixed potential at a value substantially to preclude the fiow of signals through said control channel when the amplitude of said signals is below a predetermined value, whereby the control channel output potential is controlled independently of the sign-a1 modulation and without signal distortion.

'7. The combination with an intermediate frequency amplifier, of a second detector coupled thereto and comprising an output circuit, means for deriving from said output circuit a unidirectional control potential in response to a received signal, a control channel having an amplifier tube coupled to said intermediate frequency amplifier to receive at least a portion of the signal output therefrom, said amplifier tube including a gain control grid connected in circuit with said potential deriving means, whereby the gain of said tube is controlled in response to variations in the strength of a received signal, means for preventing the transmission of signals through said amplifier tube below a predetermined signal level, a rectifier device coupled to said amplifier tube having an output circuit providing automatic volume control potentials, and means for applying said automatic volume control potentials to said intermediate frequency amplifier to control the gain therein.

8. The combination with an amplifying channel for modulated radio signals, of a signal detector coupled thereto and having an output circuit providing a unidirectional potential variable in response to the signal modulation and automatic volume control means for said signal amplifying channel comprising a control channel having an amplifier tube coupled to said signal amplifying channel substantially in parallel therewith to receive at least a portion of the signal energy therefrom, means for biasing said last-named amplifier substantially to cut-ofi' to volume control potentials variably in response to variations in signal strength above said predetermined value, and means for applying said automatic volume control potentials to said firstnamed signal amplifying channel.

RENE A. BRADEN. 

